Hi!
I have been refitting my P3A with new resistors (RC55) and one of side with new power devices (MJ15003/15004) and new VR1, since I killed them due to slipping probes (I had connected the collector of Q7 to ground).
The side without new power devices works well, but the one with new transistors doesn't.
Tests like Rod describes with 22 Ohm resistors are OK, +- 42 V on the rails, 4 mV dc offset
But then measuring voltage across the 0.47 ohm resistors (which should be about zero), I measured 38 V across R13... as well as between the collectors of Q7 / Q8
Then I also exchanged all other transistors (the BD139/140 and BC546 types), and measured again. Voltage across R13 went down to 9.3 V, as well as between collectors Q7 / Q8, but still way too high.
Amazingly nothing gets really hot.
Has anyone an idea of what to look for? I resoldered everey solder joint, checked for shorts, did not find anything...?
Bye,
Arndt
I have been refitting my P3A with new resistors (RC55) and one of side with new power devices (MJ15003/15004) and new VR1, since I killed them due to slipping probes (I had connected the collector of Q7 to ground).
The side without new power devices works well, but the one with new transistors doesn't.
Tests like Rod describes with 22 Ohm resistors are OK, +- 42 V on the rails, 4 mV dc offset
But then measuring voltage across the 0.47 ohm resistors (which should be about zero), I measured 38 V across R13... as well as between the collectors of Q7 / Q8
Then I also exchanged all other transistors (the BD139/140 and BC546 types), and measured again. Voltage across R13 went down to 9.3 V, as well as between collectors Q7 / Q8, but still way too high.
Amazingly nothing gets really hot.
Has anyone an idea of what to look for? I resoldered everey solder joint, checked for shorts, did not find anything...?
Bye,
Arndt
Hi!
You can find it at ESP, but I steal a picture:
Just one comment: I do not use A1302 / C3281 but MJ15004 / MJ15003...
I had just an idea (but I am not home, so I can't check it), that it maybe R13 itself which could be faulty...
Bye,
Arndt
You can find it at ESP, but I steal a picture:
An externally hosted image should be here but it was not working when we last tested it.
Just one comment: I do not use A1302 / C3281 but MJ15004 / MJ15003...
I had just an idea (but I am not home, so I can't check it), that it maybe R13 itself which could be faulty...
Bye,
Arndt
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.